The seven known depth cues, in descending order of effectiveness, are:
1. Stereopsis (the perception of depth in images from two laterally-displaced lenses).
2. Motion parallax (relative shift of objects due to viewer or subject motion).
3. Perspective (lines in a scene receding toward a vanishing point).
4. Occlusion (one object blocking another).
5. Relative object size.
6. Atmospheric haze.
7. Accommodation (focus).
The term “3D” is used liberally and is frequently used incorrectly when describing images on a flat 2-dimensional screen when the only depth cues may be perspective, occlusion, relative size or atmospheric haze. A true 3-dimensional image conveys a sense of depth using stereopsis or motion parallax and provides a measure of look-around ability.
Electronic-image displays are used on many products, including televisions, computer monitors, electronic-book (e-book) readers, and cell phones, and which produce flat 2-dimensional images.